`.github/workflows/deploy_unified_header.yml` needs `permissions: contents: write`

[pdimov]

Due to

https://www.stepsecurity.io/blog/hackerbot-claw-github-actions-exploitation

we'll be changing the default GHA permissions for boostorg to read-only.

Since .github/workflows/deploy_unified_header.yml does git push, it will need to be updated to contain

permissions:
  contents:
    write

(https://docs.github.com/en/actions/reference/workflows-and-actions/workflow-syntax#permissions)

I'd also recommend enabling branch protection, so that the master and develop branches can't be rewritten or deleted.